1. Field
The present invention relates to a pressurized vessel, such as a sterilizer, having a pressurized door seal. The invention is more particularly directed to such a vessel having means for precluding the door seal from being depressurized when pressure is not within a preselected pressure tolerance.
2. State of the Art
In a pressure vessel, such as a sterilizer, the interior of the vessel is typically subjected to a"cycle" or sequence of steps which may involve pressurization and/or evacuation. A problem area for such vessels is the sealing of the door, both before, during, and after the prescribed cycle. It is important that the door remain sealed during the cycle to avoid explosive equalization of pressure between the chamber and the environment and to avoid the escape of undesirable gases from the chamber.
One system that has been used to seal the doors of pressure chambers is an inflatable gasket, sometimes referred to as a balloon gasket. The balloon gasket is positioned around the perimeter of the entry to the chamber. Once the door is closed, the balloon gasket is inflated to create a positive seal between the door and the vessel.
In another system, an annular gasket is positioned in an annular channel around the perimeter of the entry of the chamber. A fluid-tight gasket chamber is defined between the gasket and an interior surface of the gasket channel. This gasket chamber is pressurized to force the sliding gasket into contact with the door. After the cycle is complete, the pressure behind the sliding gasket may be reduced to below atmospheric to draw the gasket away from the door to preclude the gasket from being stuck to the door when the door is opened. Such a pressurized sliding gasket system is disclosed in U.S. Pat. No. 3,694,962 (McDonald et al.), the disclosure of which is incorporated herein by this reference.
In such sliding-gasket systems, the chamber behind the gasket is typically pressurized by a steam supply. The steam supply may also be used as a sterilizing agent within the pressure chamber or sterilizer. The steam supply is typically connected to the gasket chamber by means of a three-port solenoid valve. In an energized condition, the solenoid valve connects the steam supply to the gasket chamber. When the solenoid is de-energized, the valve connects the gasket chamber line to an ejector. The ejector reduces pressure from the gasket chamber below atmospheric to draw the gasket away from the door to positively break the seal with the door.
A problem that exists in any pressurized sealing system is that if electrical power is interrupted to the valve providing pressure to the seal, the seal may be rapidly depressurized. If such depressurization occurs while a pressure or vacuum still exists within the pressure vessel, a rapid equalization of pressure can occur, which may involve sterilizing steam or gas being ejected from the pressure vessel. Such occurrences can be dangerous to personnel in the vicinity of the pressure vessel and destructive to the gasket or sealing member.
If the seal is pressurized by a steam supply, because of pressure and temperature conditions in the gasket chamber, a great deal of condensation can occur. It is not uncommon for the gasket chamber in a sliding gasket system to be completely filled with water. To bleed off condensate in the gasket chamber and the respective lines leading from the steam supply, a steam trap is typically connected between the steam supply and the solenoid valve. Such steam traps are designed to allow liquid water to drain without the loss of substantial amounts of steam pressure. However, if the steam supply is disrupted, pressure in the gasket chamber may be slowly bled off through the steam trap to thus depressurize the gasket chamber. Although the depressurization is not as rapid as occurs upon failure of power to the solenoid, such depressurization, if it occurs while pressure or vacuum still exists within the vessel or sterilizer, can cause dangerous or explosive conditions.
Thus, there remains a need for a pressure vessel having a valving configuration which eliminates dangerous conditions that can result upon disruptions to gasket pressurization while the vessel or sterilizer remains either pressurized or evacuated.